Electrostatic separator



Jan. 18, 1955 E C, GEAR ELECTROSTATIC SEPARATOR 3 Sheets-Sheet l Filed April 18, 1952 wis-Nro@ E. G. GEAR Jan. 18, 1955 E. c. GEAR 2,699,869

ELECTROSTATIC SEPARATOR l Filed April 18, 1952 3 Sheets-Sheet 2 INVENTO? E. C. GEAR BY C. AVrnmrw United States Patent() 2,699,869. ELEcTRos-TAric snrnnaron- Eli C. Gear, Minneapolis, Minn., assignor` tof Generali Mills, Inc., a corporation-oflDelaware- Application April 18, 1952",` SerialNo; 283,021

auf Claims. (ci. 209-.-127) The present invention relates to electrostatic separation and particularly to improved'appar-atus for precise sepa ration of organic stocks, containing a wide range oparticle types which differ only slightly one from another in their electrical characteristics.

Electrostatic separators have/been` proposed in the prior art in which material is fed in` agivendirection and an electrostatic field is produced which results in movement of selectedl particles transversely to said direction of feed. Such deviceshave worked satisfactorily with materialstin which a relatively smallnumberfoffparticle types-wereineluded and where such types differed widely in their electrical characteristics. For example, conductors could1 be reasonably well separated from hon-conductors bysuch devices. However, precise separations have not been achieved where organic, particles were involved,` or where 2 extends substantially horizontally between the frame meinbers 24. In the form` illustrated, this supporting member consists of an electrically conducting plate or lower elect-rode. A supply 4hopper 32 atone end of the device is provided with an adjustable gate 34 by means of which athin uniform stream of material maybe fed from the hopper 32 alongV the upper surface ofthesupporting electrodell.

While itis possible in some cases to obtain the desired feeding movement` along the electrode surface 30 by suitable inclination'of the surface to obtain a gravity flow, the illustrated' embodiment makes use of the inclined springs-26 and a suitable vibrator` 36 by means of which the frame members `24 and electrode 30 may be Vibrated rapidly in a direction `perpendicular to the plane of the springs 26. This direction of vibration will thus include a substantial component longitudinally ofthe plate 30 and in the plane thereof, as well as a substantial component perpendicular to such plate.

The vibrator 36 is energized through connections 38 with a vibrator power source 40.

Located above a substantial area of the lower supporting member 30 is an upper electrode 42 which serves as a means ,for establishing the desired electrostatic field above thelower electrode. This upper electrode 42 is mounted on brackets 44 secured to the frame members 24. These a wide range. of particle types of onlyslightlydiferent electrical characteristics were included.

It is accordingly `one object of-"the present` invention to provide an improved electrostatic separator of the typein which material is initially fed to one area offa supporting member and in which selectedtypesofparticles are urged to another area of the supporting member under the combined influence of the electrostatic field, the feeding means, and other factors involved;

A further object is the provision of an improved means for establishing a directional electrostatic field forsuch a device.

Still another object is the provision of a separator of this type in which a barrier of predetermined height assists in controlling the passage of selected particles from one area to another of the `supporting member.

A further object is the provision of an electrostatic separator in which at least one barrier is provided on a supporting electrode, and in which the direction of'feed, the electrostatic field and other factors` are correlated to give selected particlesof the materialrepeated opportunities for attraction above` and across the barrier;

Other objects and advantages'will b'eV apparent `from'the following specification in which certain embodiments d f the `invention are described with particular' reference-to the accompanying drawings.

In these drawings, wherein like` reference characters indicate like parts, e e e Figure 1 is a` partial perspective view of @electrostatic separator incorporatingfatures of the present invention.

Fig. `21s a` perspective view` of the upper electrode of the-,device effig. l..

Ffgp iS a partial perspective trede. ofthe device QfFig, 1.

Fig. ,4 isan enlargedpartial and perspective view of the view of the lower elec,-

device of Eig. 1 showing. one adiustmenit-of the electrodes Fie 5. is a View similiar to Eig. 4 slwwinsv another adjustment of the device ofEig, `l.

Fis,- 6 i a Secticnalview on the line 6-6 of Fis- 2- Fis.. 7` is a top View of thedevice 0i Fis-` 1. Eig.,8 is. a. partialperspective view similar to Fig. l of another embodimntrflhe invention.

t Fig., 9 is a top. view Qfjthe device of Eig. 8', ,and

Fig.10 `is atopwiew ofl a modifledernbodiment, with a-` portion `.of the upperelectrode brokenaway for clarity.

As shown in Figs. 1f through 7 a preferred form of separator according to the `present invention includes a supporting ibase 22 above which Suitable ,frame members 24 are supported by means of inclined springs 26 .and"2&.

1M-supporting member 30 forrtheimaterial tobeyseparated vertical supports 44 are provided with vertical slots 46 permitting vertical adjustment of the upper electrode 42 in the manner described below. In Fig. l the lower electrode 30` and frame members 24 are shown as grounded at48, while the upper electrode is maintained at a desired relative potential difference with respect to the grounded lower electrode by means of a connecting wire Si) and a voltage source 52. This electrical supply unit 52 may be provided with a'volt meter or other indicator 54 and an adjusting rheostat 56 for selection of the desired voltage and field strength.

According to the present invention, the material from the supply hopper 32 is fed across a predetermined initial area of the supporting member or lower electrode 3l). To guide the material to the desired first area of the plate, an inclined baille 58 is located near the feed hopper 32 to guide the stock along a feed path which extends longitudinally of the lower electrode 30 in this particular case and adjacent one edge 62 of the device. This feed path'or first area of the plate is indicated at in Fig. l. Ifdesired, the width of hopper32 and gate 3,4 may be made to correspond to the width of area 6l) in which case no diagonal baille 58 would be needed, and the ilow of material areasofthe plate` to obtain the desired classification. Ac-

cording to a further aspect of the invention, the different areas of the plate are separated by one or more barriers or baille members as indicated at 64, 66, and 68. These barrier members are of predetermined height and require that the types of particles to be collected in the areas beyond a given barriermust be urged upwardly (by a combination of the feeding means, electrostatic field, and other factors) higher than the predetermined height ofthe bar rier inorder to reachsuch other areas. In this case, a second or intermediate collecting area of the plate extends longitudinallybetween the barriers l6d and 66 as indicated at 70. A further area of collection is indicated at 72 between the barrier 66 and the baffle member 68, while' a nalareaof collection is shown at 74 between the baffle member 68 and the opposite or second longitudinally extending lateral edge of the lower electrode 30. The fractions segregated in the different areas 60, 70, 72, and 74may then be fed by spouts 77 to different collecting means such as receptacles or chutes 79.

As shown in Fig, 3, the baille members 64, 66', and68 in this particular embodiment extend longitudinally of the lower electrode 30 substantially parallel to the direction of feed of thestocl. Thus the stock passing down the firstiarea 60 of electrode 30 will have repeated opportunities fonindividual particles` of the desired 'types to bepro- Paienied Jian. 1s,` 1.955.r

jected upwardly to a sufficient height to clear the first bafe member 64 and reach at least the second area 70. In this embodiment, the baffles are of electrically conducting material connected to the lower electrode and thus maintained at the same potential as the latter. Because they project above the lower electrode and are thus closer to the upper electrode, the electrostatic field above each baiiie will be more intense than at other areas of the electrode, a factor which is believed to contribute to precision of separation in certain cases. Should a more uniform field be desired, insulating baflies may be used.

According to another aspect of the invention, the de sired separations are facilitated by providing baflie members of different predetermined heights. While the rela tive arrangement of the different baffles may vary dependA ing upon particular circumstances and a particular stock which is under classification, the embodiment illustrated in these drawings utilizes successively higher baflies so that the first barrier 64 is lower than the second barrier 66, while the third bafiie member 68 is higher than barrier 66. Thus all particles which have an opportunity to be projected upwardly high enough to clear the first baffle 64 and which by the combined effect of the electrostatic field, feeding means, and other factors acquire a sufficient transverse component of motion, will be enabled to reach the second area 70 of the lower electrode.

Some of the particles reaching this area 70 will have electrical characteristics which enable them to be projected above the higher second baffle 66 and across to the next area 72. Certain of the particles reaching the area 72 may then have electrical characteristics which permit them to be projected upwardly even higher and pass over barrier 68 into the final collecting area 74. Thus the use of barriers of different heights can contribute effectively to the precise separation of types of particles which differ only slightly in their electrical characteristics.

Reference has been made above to the necessity of giving the selected particles of material a component of motion transverse to the original direction of feed through the combined action of the feeding means, the electrostatic field, and other factors, such as gravity. In the present embodiment of the device, since the feeding means has been described in such a manner as to provide the particles with components of ymotion longitudinally of the electrode 30 and perpendicularly to the plane of the electrode and since this particular embodiment is substantially horizontal, the necessary transverse component of motion must be obtained by means of the electrostatlc field. The directional effect of this field is obtained by the particular construction of the electrode 42.

Other forms of upper electrode have been proposed in the past for use in obtaining the desired selective transverse movement of certain types of particles. While such prior devcies may be used in combination with suitable barriers on the lower electrode according to certain aspects of the invention, the present invention also includes a specific improved construction for such an upper electrode. This upper electrode 42 is shown in Fig. 2 and includes brackets 76 at one edge of the electrode, provided with holes'78 through which a clamping bolt may be passed to secure the brackets 76 and corresponding electrode edge to the supports 44 at one edge of the lower electrode 30. The other edge of the upper electrode 42 includes similar brackets 80 provided with openings 82 for a similar purpose.

vTo obtain the desired directional effect for the electrostatic field, the undersurface of electrode 42 is provided with a series of transversely extending substantially parallel corrugations indicated generally at 84. As illustrated in Fig. 7, these corrugations 84 are inclined from the path of feed in the first area 60 of the lower electrode toward the opposite edge 75 of the lower electrode in a direction extending not only transversely of the device In the form shown in Fig. 2, the front and rear walls intersect each other along transverse lines 90 representing the lowest region of each corrugation. The rear and front walls 86 and 88 preferably have different slopes or inclinations with respect to the plane of the upper electrode. It is considered important to have a much steeper slope for the rear wall 86 than for the front wall 88.

In the embodiment shown in the drawing, the rear walls 86 are substantially vertical, while the front walls 88 are rather gently inclined and have a slant height (i. e., the distance measured from the line of intersection 90 to the surface of the upper electrode along a line perpendicular to line 90) which is at least twice as great as the vertical depth of the rear wall 86. The particular spacing of the corrugations is such that the gently sloping forward walls 88 reach the plane of the upper electrode just at the foot of the rear wall 86 of the next section and thus intersect the rear wall as well as the plane of the electrode along a series of transversely extending lines 92.

The fact that the specific configuration and especially the rearward angular orientation of the corrugations with respect to the original direction of feed will produce transverse movement of selected particles from the first area 60v of the lower electrode toward the second area 70 and the farther edge 75 of the plate is particularly surprising because of the suggestion in the prior art that the material particles would tend to follow the more intense areas of the field which are presumed to lie directly beneath the lowest portions 90 of the corrugations. If this were the case, the particles which originally have a longitudinal component of motion due to the inclined springs 26 and 28 and vibrator 36 would be expected to move from the original feed path in the first area 60 toward the edge 62 of the electrode. While the particular theory of operation of the construction shown in the drawings is therefore not completely understood (but is believed to involve the relative difference in slopes of the front and rear walls of the corrugations 84), the fact remains that the particular construction does produce movement of the particles from the region 60 toward the opposite edge 75 of the lower electrode. Y

In Fig. 7, the original direction of feed is indicated generally by the arrow 96 along the first area 60 of the plate. The effect of the corrugations 84 on the upper electrode thus tends to move certain selected vparticles generally toward a path 98 which extends transversely of the lower electrode toward the edge 75 along a line generally perpendicular to the corrugations 84. Because the v device of Figs. l through 7 includes barriers 64, 66, and

the area above the lower electrode.

but also having a substantial component rearwardlyor opposite to the original direction of feed of the masis' 68 which are substantially parallel to the original direction of feed, indicated by arrow 96, the corrugations of the upper electrode in this case are inclined with respect to the barriers by the same angle 94 previously referred to as defining the inclination of the baffles with respect to the direction of feed.

Certain of the stocks which can be separated by the device described above can best be handled by provision of a substantially uniform electrostatic field throughout For this purpose the apparatus is adjusted as shown in Fig. 4 so that all portions of the upper electrode are substantially the same distance above the lower electrode.

In other cases, with certain stocks, it may be desirable to have a field in which the general intensity is non-uniform. For this purpose the device maybe adjusted as shown, for example, in Fig. 5 in which the edge of the upper electrode above the first edge 62 of the lower electrode is closer to the electrode than the opposite edge of the upper electrode which is'located above edge75 of the lower electrode. By this arrangement, the general intensity of the electrostatic field is greatest along the original path of feed and gradually decreases as one moves transversely toward 'the opposite edge 75.

As pointed out above, the transverse component of motion of the particles to take them across barriers 64, '66, and 68 is provided primarily by means of the particular configuration of the `upper electrode and the resultingvdirectional effect of the electrostatic field, in the device lof Figs. 1 through 7. It is possible in some cases, however, to practice certain aspects of the present invention by an arrangement in which the relative orientation of the barriers, the direction of feed, the feeding means, and the type vof electrostatic field are somewhat different. l

For example,` in the device of Figs. 8 and 9, the sepagoasgs'es arator includes a lower electrode or supportingV plate 100 which may be mounted on inclined springs for vibration in the same manner as electrode 30of the/pres ceding embodiment. electrode has an adjustable feed gate 104 for starting athin uniform stream of material acrossthe lower electrode. In this case, a single barrier 106 ofpredetermined height is illustrated as extending at an angle to the longitudinal axis or direction of feed of the plate 100.

This barrier 106 is preferably made of insulatingfmaterial in order to offer the least possible interference with `the uniformity of the electrostatic fieldl to be created above plate 100; Barrier 106 is inclined from one edge 1'0Sofelectrode 100 toward the opposite edge 110. Thus thel barrier 106 is disposed at an acute angleV with' respect tothe direction of feed of the material along plate 100. To state the condition another way, the path of`movement of the stock under the effect of.` the feeding means (sincerit is similar to that of the devicein Fig. 1) will have a very substantial component of motion parallel to the barrier, althoughY in this case the` path offeed is` notY exactly parallel thereto. In other: words, the angle between the feed path and barrier (as shown `at 115 in, Fig. 9) is substantially lessthan 90l degrees. The net` result will be to retain those particles whichA are not projected high enough to clearl barrier 106 onthe original side of the barrier in the first or initial area 112` of plate 100.

` The angular inclination of the barrier willresult` in movement of the particlestransversely toward edge 11,0 of this. electrode asthey are fed' along the latter.` Barrier 106 divides the plate into aiirst area112 mentioned above anda second area 114," into which selected particles may by projected byy the particularcombination effect of the electrostatic. field, the feeding means, and the angular orientation of' the barrier. Separate collecting means for the, fractions segregated in the two areas are provided as in the previous embodiment.

In this case the upper electrode 116u may be in the form of a flat plate spaced substantially uniformly above the lower electrode 100 and maintained at` a relative difference of potential with respect thereto by means similar to that shown in Fig. l; ThusA a substantially uniform field will be maintained between the electrodes and this field Will have` no particular directional effect.

However, the longitudinal component of vibration of the lower electrode 100 will tend to project individual particles across the barrier 106. The particles can not be projected,` however, unless they are also urged upwardly a distance greater than the predetermined height of lbarrier 1061 This upward movement or urgeA is controlled by adjustment of the electrostatic iieldstrength spo `that particlesof the desired selected type will "be lifted sufficiently to clear the barrier 106 while other particles will remain in the original area 112of the lower plate.

Because the direction of longitudinal movement imparted by the feeding rneanshas` at substantial component parallelto the barrier 106, the materialwhich 1s not sufliciently charged initially to be'A projected above and across the barrier will have further opportunities for obtaining the necessary induced charge as the particles are fed along the plate and retained by the barrier. Thus by the time the stock has been fed from the hopper 102 to the remote end of the electrode 100, every particle of the desired selected type should have had an adequate opportunity to acquire a suiiicient induced charge to be urged upwardly a distance which will permit it to clear the barrier 106 under the combined influence of the electrostatic field and the feeding vibrations of the lower electrode.

The modified embodiment of Fig. l() is similar in principle to the device of Figs. 1 through 7, except that here the lower electrode 118 has a hopper 120 and adjustable feed gate 122 f the same width as the tirst area or feed path 124. Thus the stream of materlal fed from hopper 120 will not be compressed laterally as it moves along the rst feed area 124.

Electrode 118 has one edge 126 angularly inclined away from the direction of feed along area 124 in order to provide a second area 128 at one side of the first area. A barrier 130 separates the two areas 124 and 128. Similarly, a third area 132 is separated from area 128 by a barrier 134, while a fourth collection area 136 is separated from area 132 by a longitudinal barrier 138.

A hopper 102 at one end of the- 6 Y Upper` electrode 140v is provided with angular corru-4 gations or steps 142 on its undersurface, just as in the case ofelectrode 42 of Figs. 1 to 7. Thus the desired particle typesv are segregated in the respective. collecting areas as a result offselectivelateralY displacement across the respective barriers.v

According to the foregoing description, a number of embodiments of the present invention have been disclosed which substantially accomplish the, objects set forth at the beginning of this specification. Since minor variations and changesf in the exact details of construetion will be apparentto persons skilled inthis` iield, it is intended that this invention shall cover all such changes and modifications as fallwithin the spirt'and scope of the' attached claims.v

Now, therefore, I claim:

1. An electrostatic separator comprising an electrically conducting supporting plate, meansl for feeding a thin uniform stream` of materialV along a given path across the upper surface of the plate, an upper electrode spaced above the` plate and establishing an electrostatic field between the plates, said upper electrode havington its undcrsurface a series of parallel downwardly projecting corrugations extending across the path of'feedl at an acute angle with respect to such path, the angular orientation of the corrugations producing a field urging selected particles of material angularly across said path toward a direction generally` perpendicular to the corrugations, andmeans for collecting separately a first fraction including particles which continue along the original feeding path and at least one-second fraction including particls which have been urged laterallyv away from said pat 2. An electrostatic separator according toyclaim l in which each corrugation includes `a rear wall facing back toward the portion ofthe path from which the material is fed and a forward wall facing in theA opposite direction, said walls being angularly disposed `with respect to the plane of the upper electrode.

3. An electrostatic separator according to` claim 2 in which said front and' rear walls intersect each other below the plane of the upper electrode and are inclined at different angles to the plane of the upper electrode.

4. An electrostatic separator according to claim 3 in which said rear wall is inclined more, steeply than saidiirst wall.

5. An electrostatic separatorv according to claim 4 in which said rear` wall is substantially vertical and said front` wall slopes gently toward the plane of the upper electrode.

6. An electrostatic separator according to claim l in which the upper electrode is inclined with respect to the lower electrode so that the portions of the upper electrode corrugations farthest from the original path of feed are also spaced farther from the lower elec trode than thosel portions of` the corrugations nearest the` original path of feed. 7. An electrostatic separator according to claim 1 having at least one barrier of predetermined height extending across the upper surface ofv the lower plateV and dividing the latter into a iirst area in which the material is originally fed and a second area which receives those particles projected over said barrier under the action of said feeding means and said field.

8. An electrostatic separator comprising an electrically conducting supporting plate having a smooth upper surface throughout its major area, means for feeding a thin uniform stream of the material along a given path across the smooth upper surface of said plate, means including the plate for establishing an electrostatic field above the plate urging selected particles upwardly from the plate, at least one barrier of predetermined height on the upper surface of the plate within said field and extending along the path of movement of said particles, said barrier dividing the material into a first fraction consisting of particles remaining on the original side of said barrier, and at least one second fraction which consists `of particles which are attracted upwardly beyond said predetermined height and which thereby move across said barrier, and means for collecting separately said first and second fractions.

9. An electrostatic separator according to claim 8 having two of said barriers extending across successive portions of the path of movement of said particles, the first barrier having a height different from that of the escasas second barrier, and. means for vcollecting separately the fraction which remains between the barriers and the fraction which passes both barriers.

10. An electrostaticseparator according to claim `9 in which the first barrier is lower than the second barrier.

11. An electrostatic separator comprising a supporting plate having a smooth upper surface throughout its major area and an edge, means for feeding a thin uniform stream of material across a substantially smooth, unobstructed portion of the upper surface of said plate, means establishing an electrostatic field above the plate urging selected particles upwardly from the plate, said particles being moved by said feeding means along a path toward the edge of the plate under the combined influence of said feeding means and field, a barrier of predetermined height on the upper surface of the plate within the field, said barrier extending across said path of movement of the particles and dividing the plate and field into a first area containing a first fraction consisting of particles remaining on the original side of the Vbarrier and a second area containing a secondV fraction consisting of particles which are projected upwardly beyond said predetermined height and which thereby move across said barrier, and means for collecting separately said first and second fractions.

12. An electrostatic separator comprising a supporting plate having a smooth upper surface throughout its major area a barrier of predetermined height extending across said plate and dividing the plate into first and second smooth-surfaced areas, means for feeding a thin uniform stream of material across the first area of the plate, means establishing an electrostatic field above said barrier and thereby urging selected particles upwardly from the plate, at least one of said feeding means and electrostatic field means urging selected particles from the first area to the second area, and means for collecting separately the particles of material which are projected upwardly above said predetermined height and thereby reach said second area of the plate.

13. An electrostatic separator according to claim l2 in which the feeding means urges the material in a direction having a substantial component parallel to said barrier. f

14. An electrostatic separator according to claim 13 in which the feeding means urges the material in a direction parallel to said barrier and in which the electrostatic field urges the material transversely from said first area toward said second area.

. 15. An electrostatic separator according to claim 12 having a second barrier extending across the second area of the plate and dividing such second area into an intermediate portion lying between the barriers and a final portion lying beyondthe second barrier, said second barrier havinga height different from that of the first barrier, and means for collecting separately the fracl tions of material reaching said intermediate portion Vand said final portion.

16. An electrostatic separator according to claim l in which the second barrier is higher than the first barrier.

17. An electrostatic Vseparator comprlsing. an electrically conducting supporting plate having Aa smooth upper surface throughout its major area, a barrier of predetermined height extending across said plate `and dividing the plate into first and second substantially smooth-surfaced, unobstructed areas, means for feeding a thin uniform stream of material in a given path across the first area of the plate, means establishing an electrostatic field above said barrier and thereby urging selected particles both upwardly from the plate and transversely across said barrier to said second area, the angle between said feed path and barrier being substantially less than degrees and thereby feeding along the barrier that portion of the material which reaches the barrier but is not projected upwardly high'enough to clear it, first collecting means at the end of the barrier for separate removal of the portion which remains on the original side of the barrier in said firstarea, and additional collecting means for separate removal of those particles which pass over the barrier and reach the second area.

18. An electrostatic separator comprising a lower electrode having a substantially smooth upper surface throughout its major area bounded by laterally spaced first and second longitudinally extending edges, means for feeding a thin uniform stream of material along a longitudinal path on the upper surface of the electrode adjacent said first edge, means establishing an electrostatic field urgng selected particles of material transversely of the electrode toward said second edge during such feeding, at least two longitudinally extending barriers on the upper surface of the lower electrode between said feeding path and said second edge, said barriers being separated by an intermediate smooth-surfaced collecting area, and one of said barriers projecting farther above the electrode surface than the other, and means for collecting separately the material received in said intermediate collecting area.

19. An electrostatic separator according to claim 18 in which the barrier nearest the feeding path is lower than the barrier nearest the second edge.

20. An electrostatic separator according to claim 18 having three substantially parallel longitudinally extending barriers between the feeding path and second edge, the barriernearest said path being lower than the intermediate barrier, and the barrier nearest the second edge being higher than the intermediate barrier.

References Cited in the file of this patent UNITED STATES PATENTS Australia Dec. 12, 

